I. Field of the Disclosure
The technology of the disclosure relates generally to charging a battery of portable electronic devices from Universal Serial Bus (USB) chargers.
II. Background
Portable electronic devices, such as smartphones, tablets, laptop computers, and the like, can be powered by rechargeable batteries that need to be recharged periodically. Universal Serial Bus (USB) is an industry standard that defines the cables, connectors, and communication protocols for data and power transfers among personal computers and electronic devices. Thus, USB ports have been used as both data transfer and charging ports to charge rechargeable batteries of electronic devices. The convenience of drawing current from USB ports on personal computers has led to the creation of various types of USB chargers designed for charging portable electronic devices using the same USB cables as used for personal computers.
In this regard, FIG. 1 illustrates a typical USB physical connection between a portable electronic device 10 and a USB charger 12. On one end, the portable electronic device 10 is embedded with a receptacle 14. On the other end, the USB charger 12 exposes a USB 3.x receptacle 16. A detachable USB cable 18, with a plug 20 on one end and a plug 22 on the other end, connects the portable electronic device 10 to the USB charger 12. A standard USB receptacle and connector, including the plugs 20, 22, and the receptacles 14, 16 in FIG. 1, have at least VBUS, GND, D−, and D+ pins 24, 26, 28, and 30. This is shown, for example, in the detachable USB cable 18. The VBUS pin 24 and the GND pin 26 are used for charging purposes, while the D− and D+ pins 28, 30 are designed for protocol handshakes and data transfer. The VBUS and GND pins 24, 26 are by design longer than the D− and D+ pins 28, 30, so that the VBUS and GND pins 24, 26 will make contact before the D− and D+ pins 28, 30 when the plugs 22, 20 are attached to the receptacles 14, 16, respectively. The USB 3.x receptacle 16 also contains a SSTX− pin 32, a SSTX+ pin 34, a SSRX− pin 36, and a SSRX+ pin 38 dedicated for USB 3.x SuperSpeed connectivity. The SSTX−, SSTX+, SSRX−, and SSRX+ pins 32, 34, 36, and 38 are not used when the plug 20 is attached to the USB 3.x receptacle 16.
In addition to protocol handshakes and data transfer, portable electronic devices use the relative voltage and/or current variations between D− and D+ pins to detect different types of connected USB chargers. A USB charger is deemed standard compliant if configuration and voltages of the D− and D+ pins meet the specifications of USB battery charging specification revision 1.2 (BC1.2), and non-compliant otherwise. BC1.2 defines a plurality of compliant charger categories, including Dedicated Charging Port (DCP), Charging Downstream Port (CDP), and Standard Downstream Port (SDP), among others. Following the BC1.2 algorithm results in most non-compliant chargers being detected as SDP and current draw being limited to a current level specified in BC1.2 (e.g., ISUSP.)